Overall, I count this as a very good upgrade, although some features could be a lot easier to work with.

I’m not sure why the reviews are bad but the 820 has been great huge upgrade from 500.

Great upgrade (finally, for me) from the Edge 500.

As a conclusion, I could say Edge 820 is excellent, but I'm not sure if it's worthy upgrading from 810.

Great upgrade over the 810

As a previous owner of Edge 810, I found Garmin Edge 820 a good upgrade in screen resolution, internal memory capacity (although lost capacity for external memory card) and some software improvements

So I loved it during those few months where it worked as it should most of the time.